Plastic printing plate and method for manufacture



Dec. 7, 1965v F, M, JERNT 3,221,654

PLASTIC PRINTING PLATE AND METHOD FOR MANUFAGTURE Filed Sept. 22. 1960 5Sheets-Sheet 1 FIG. l

24 5o FGV@ 50 FIG, 5

JNVENTOR. Fred M. Jamf BY am, YM

' orneyS Dec. 7, 1965 F. M. JERNT 3,221,654

PLASTIC PRINTING PLATE AND METHOD FOR MANUFACTURE Filed Sept. 22, 1960 3Sheets-Sheet 2 30 3Q FIG. 6 34 2o 7 l' AH. ,.'A

1111/111111 n n 11n', n l ,1111/11/11 527 FIG .9 /24' INVEN TOR.

F. M. JERNT Dec. 7, 1965 PLASTIC PRINTING PLATE AND METHOD FORMANUFACTURE Filed Sept. 22, 1960 3 Sheets-Sheet 5 n Fm. l5

INVENToR.

M. Jmi

Fred

United States Patent O 3,221,654 PLASTIC PRINTING PLATE AND METHOD FORMANUFACTURE Fred M. Jernt, Chicago, Ill., assigner, by mesneassignments, to Dynamics Corporation of America, a corporation of NewYork Filed Sept. 22, 1960, Ser. No. 57,757 7 Claims. (Cl. 101-401.1)

This invention relates to the art of printing plates for use with rotaryand the like printing presses and it relates more particularly to aprinting plate formed of sheet plastic and -to a new and improved methodfor the preparation of same.

It is an object of'this inventionto produce printing plates of sheetplastics and -it is a related object to provide a simple and inexpensivemeans for producing plastic printing plates of the type described fromwhich copy of good quality can be secured.

These and other objects and advantages of this invention willhereinafter appear andfor purposes` of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawings in which- FIG. l is a schematic sectional elevational viewshowing the arrangement of elements in an initial step in thefabrication of a plastic printing plate in accordance with the -practiceof this invention; FIG. 2 is a schematic sectional elevational viewshowing the arrangement of elements in an intermediate stage in thefabrication of the plastic printing plate;

FIG. 3 is an enlarged sectional elevational view of the elements used inthe fabrication of a plate as they appear immediately prior to imagingthe plastic sheet;

FIG. 4 is a schematic sectional elevational View showing the arrangementof elements in a final stage in the fabrication of the plastic printingplate;

FIG. 5 is a fragmentary sectional elevational View of a plastic printingplate prepared in accordance with the practice of this invention;

FIG. 6 is a schematic sectional elevational View similar to that of FIG.4 illustrating the preparation of a plastic printing plate embodying thefeatures of this invention;

FIG. 7 is a sectional elevational view of a fragmentary portion of theplate produced in FIG. 6;

FIG. 8 is a fragmentary sectional elevational View of a modification inthe printing plate of FIG. 7;

FIG. 9 is a schematic sectional elevational view of a 4modification inthe arrangement of elements illustrated in FIG. 4 for the production ofa finished plastic printing plate;

FIG. 10 is a fragmentary sectional elevational view of the plasticprinting plate produced in accordance with PIG. 9; t I

FIG. 1l is a perspective view in section of the construction embodied inthe ends of the plastic printing plate of this invention for use lin onemeans for mounting the plates onto the cylinder of a printing press;

FIG. l2 is a perspective view of a saddle which can be used as a meansfor mounting the plastic printing plate on the plate cylinder of arotary printing press, showing the saddle in collapsed position, and

FIG. 13 is a -perspective view similar to that of FIG. l2 with thesaddle in position of use with a plastic printing plate of thisinvention mounted thereon.

Briefly described, the concepts of this invention reside in thepreparation of a porous matrix by conventional practice of molding asheet formed of cellulosic pulp on the type set in a suitable framewhereby the cellulosic pulp conforms to the surface to form the mirrorimage in relief on the underside thereof corresponding to the type. Whenthe cellulosic pulp has been set, the imaged matrix is removed from theframe for use in the prepalCe ration of one or more plastic printingplates in accordance with the practice of this invention.

The porous matrix is then mounted with its imaged surface outermost on aperforated support having communication with a vacuum source whereby avacuum can be drawn through the entire area of the matrix. A sheet ofthermoplastic resinous material, heated to a temperature sufficient toenable plastic flow, is brought into contact with the imaged surface ofthe porous matrix with a sealing relationship between the edges. Air isexhausted through the matrix whereby the heated plastic is forced intointimate molding relationship with the surface of the matrix to causedisplacement of the plastic into the image in relief in the surface ofthe matrix thereby exactly to conform with the imaged surface of thematrix. The plastic sheet is held in molding relationship with theimaged surface of the matrix until the plastic has set upon cooling andthereafter the plastic sheet can be removed from the matrix to provide aplate having the printed image formed as a direct image in offset in thesurface thereof. The edges of the formed plastic printing plate can thenbe trimmed, if necessary, for fitting onto a saddle or other means bywhich the plastic printing plate is mounted onto the press and the endscan be processed for engagement by `clamping means by which the plasticprinting plate is held taut Vto conform to the curvature of the saddleor the plate cylinder on the printing press.

Having broadly defined the concepts of this invention, detaileddescription will now be made of the practice thereof in its variousmodifications. As representative of the vacuum means, reference will bemade to a vacuum pan 1t) covered with a flat perforated plate 12supported by grids 14 and having an outlet opening 16 in the bottom sideof the vacuum pan in communication with an exhaust means (not shown) forexhausting air from the pan and to pull a vacuum over elements mountedin Vsealing relationship on the surface of the perforated plate 12. `Ahold-down frame for maintaining a sealing relationship about the edgesof the elements mounted on the perforated plate is indicated by theframe bars 18.

The porous matrix 20 is positioned on the surface of the perforatedplate 12 with the imaged surface 22 in relief uppermost in the plate.Detailed description of the imaged matrix will not be given since it isof conventional construction formed of a porous sheet of paper pulpmolded onto the type set within a frame whereby the pulp fibers of thematrix enter the depressions exactly to conform with the surface of thetype face to form a reverse image in relief on the engaged surface ofthe porous matrix. The imaged matrix, which can also otherwise beformed, is characterized by the porosity of paper to enable air or vaporto be drawn throughout the area thereof and preferably with the faceopposite the imaged surface being at for more substantial support on theat surface of the perforated plate 12.

In the preferred practice of this invention, illustrated in FIG. l, theplastic sheet 24 is mounted in spaced relationship with the imagedsurface 22 of the porous matrix 20 and a heating means 26 is temporarilydisplaced therebetween for generation of an overall heat patternsimultaneously to heat the adjacent surfaces of the plastic sheet 24 andthe imaged surface 22 of the por-ous matrix. The desired heat can besupplied by electrical resistance heaters in the form of Calrod units orthe like. Instead, use can be made of a heated plate or of hot air orvapor or the like heat transmission means introduced into the spacebetween the plastic sheet and the porous matrix uniformly to heat theadjacent surfaces over the entire area.

When the plastic sheet 24 has been heated to a temperature sufiicientfor plastic ow in response to applied force, such as to a temperature of350 F. or above for polyethylene and corresponding temperatures forother plastic materials, the heat means 26 ishwithdrawn from between theheated plastic sheet and the porous matrix and the plastic sheet, whilestill in the heated state, is brought into surface contact with theimaged surface of the porous matrix. The edges of the plastic sheet andthe porous matrix are held in sealing relationship with the perforatedplate 12 by the clamping frame 18, as illustrated in FIG. 2 of thedrawings.

When the described sealing relationship has been established, air isexhausted from the vacuum pan through the opening 16 for correspondingwithdrawal of air through the porous matrix 20 whereby the softenedplastic material is drawn by one or the other lof the combination offorces including vacuum on one side and atmospheric pressure on theother to cause plastic to enter into the recesses 27 of the imagedsurface of the porous matrix t-o cause the adjacent surfaces of theplastic sheet exactly to conform to the imaged surface of the matrix, asshown in FIG. 6 of the drawings. It will be understood that the entranceof the plastic into exact conformance with the imaged surface of thematrix may result from flow of the plastic material while in a stage ofplastic iiow or by deformation of the sheet while still in the plasticstate, but it is believed that exact conformance to embody each detailof the imaged surface results from a combination of plastic iiow anddeformation in response to forces acting throughout the-entire area ofthe sheet, including the base of each crevice or recess in the imagedsurface through which vacuum is active as a deforming force.

It is desirable to perform the described molding operation as quickly aspossible after heating, otherwise heat loss will occur from the exposedsurfaces thereby to make it more difficult to effect flow of the plasticmaterial through the innermost recesses of the imaged matrix withcorresponding loss of detail in the image that is formed in offset inthe adjacent surface of the plastic sheet.

Heat loss from the molded plastic sheet to the atmosphere and to thematrix and through the matrix to the perforated plate and the likeoccurs sufficiently rapidly to reduce the plastic of the sheet to atemperature suicient to set the image so that the imaged plasticprinting plate 30 can be unclamped for separation from the surface ofthe matrix in the matter of a few seconds, but it is best to retain theelements in molding relationship for a longer period of time, such asfor fifteen or more seconds, to insure elimination of the possibilitiesof elastic memory.

When the plastic has set and the molded plastic printing plate 30 isremoved from the mold, it will be found that the surface which wasadjacent the imaged surface 22 of the matrix will have the imagereproduced onto the surface of the plate as a direct image 32 oset fromthe surface of the plate. Thereafter, when the imaged plastic printingplate is mounted onto the cylinder plate of a printing press with theoffset image 32 outermost, the offset image can be used as aConventional lead plate of the type heretofore cast from the matrixwherein the molded plate is inked and brought into surface contact witha web of paper advanced through the press for the transfer of the inkimage from the plate onto the paper, in accordance with the normal pressoperation.

While it is preferred to preheat the surface of the matrix incombination with the sheet of plastic material, it will be understoodthat the surface of the matrix can be heated separate and apart from thesheet of plastic but preferably immediately prior to bringing the sheetof plastic into molding relationship with the surface. Such preheat ofthe surface of the matrix operates to increasey the temperature of thesurfaces whereby lesser differential in temperature will exist betweenthe imaged surface of the matrix and the surface of the plastic sheetbrought into molding contact therewith. As a result,

the surface of the plastic will be relatively free of cold shock.Instead, it will be retained in a plastic state for a greater length oftime to extend plastic flow for a time sufficient to permit entrance ofthe plastic into the innermost recesses of the image in relief in thematrix. Preheat of the imaged surface of the matrix is not essential tothe practice of this invention, especially when the sheet of plasticmaterial embodies suticient cross-section or body to retain the heatintroduced therein for maintaining the surface in a desirable state ofplastic flow or else is heated to a sufficiently high temperature tocompensate for the heat loss to the surface of the matrix when broughtinto molding relation therewith. Under such circumstances, the sheet ofplastic can be heated separate and apart from the matrix. In any event,it is desirable uniformly to heat the sheet of plastic throughout thesurface area thereof.

As the plastic sheet of which the printing plate is formed, use can bemade of sheet stock formed of such thermoplastic resinous materials aspolyethylene, polypr-opylene, polyvinyl acetate, cellulose acetate,cellulose propionate, polytetraiiuoroethylene, polyvinylidene chloride,polyvinyl chloride, rubber hydrochloride, and the like. The sheet can befabricated of the clear plastic, with or without plasticizer, or use canbe made of a filled plastic wherein use is made of such conventionalllers as clay, calcium carbonate, silica dust, titanium dioxide and thelike. Modification to include pigments and other coloring agents toimpart color to the plastic is also possible.

Use can be made of a sheet of plastic having a thickness within therange of from 0.003 to 0.020 inch. A sheet of the thickness described isimmediately and substantially completely responsive to the pressureconditions existing for the conformance with the portions in relief inthe matrix to form a printing plate 30 of the character illustrated inFIGS. 6 and 7. A plate formed of such thin plastic sheet stock can beeasily bent while cold to conform to the curvature of the cylinderprinting press or the saddle on which it is supported for clamping ontothe press.

When such thin sheet stock is employed, the portion offset in the matrixto form the positive image will usually find its counterpart in relief,as illustrated by the numeral 34, in the backside of the plate such thatlittle, if any, backing exists for the offset imaged portions of theplate. Satisfactory performance can be secured by such plate, especiallywhen the imaged portions are relatively free of continuous offsets ofsubstantial area. However, when the area of offset is substantial, asillustrated by the offset 36 in FIGS. 6 and 7, the thickness of theplastic across the printing surface will be unsufiicient by itself andwithout other support to resist the pressures existing upon contact withthe ink rollers for inking the image or upon contact with the surface ofthe paper pressed into contact with the inked image such that incompleteimage reproduction will sometimes be experienced.

Further concepts of this invention reside in the means whereby suchpossible limitations in the performance of printing plates of plasticcan be overcome without disturbing the ease and simplicity ofmanufacture and utilization of plastic printing plates of the typedescribed.

In accordance with one concept, the possible decicncies previouslydescribed can be overcome by filling the portions in relief in thebackside of the plastic printing plate with a material which can beconverted to a hardened or set stage whereby the pressures applied tothe printing face of the plate can be transmitted through the filling 40to the support thereby to resist deformation of the imaged portions. Forthis purpose, use should be made of a material which can be applied in afiuid or plastic stage to enable the material to be introduced or forcedinto the recessed portions substantially completely to fill the portionsin relief, as illustrated in FIG. 8.

Representative of the materials which can be used as the liller 40 areliquid polymerizable synthetic resin forming materials either in amonomeric stage or in a low stage of polymeric growth or a polymericresinous material dissolved in such monomeric material or low polymericmaterial but which materials are capable of advancement rapidly to a setor hard stage after being introduced into the relieved portions of theplate.

Instead, use can be made of a heat hardenable thermoplastic resinous orpolymeric material, wax, bituminous material or the like which ischaracterized by a stiifened or hardened stage at ambient temperaturebut which is reducible to a iiuid or plastic stage at elevatedtemperatures which are still sufficiently low to enable introductioninto contact with a molded sheet of plastic material substantially toiill said recessed portions to present a relatively iiat surface acrossthe backside of the plate without raising the temperature of the plasticmaterial to a state where the image will be deformed by elastic memory.

`It will be suiiicient if such filler materials are introduced at atemperature less than about 200 F. and preferably at a temperature lessthan 150 F.

The iilling material 40 can be introduced as an incidence to the moldingoperation while the sheet of plastic material is in molding relationwith the matrix for support. Under such circumstances, the fillingmaterial may be introduced at higher temperatures. Instead, the fillingmaterial can be introduced, especially while in a liquid state, afterthe printing plate has already been formed and separated from the matrixto make the molding equipment and/or matrix immediately available foruse in the fabrication of additional printing plates.

In a preferred concept of this invention, use is made of a sheet ofplastic having sufficient thickness to provide for temperaturedifferential through the cross-section whereby the surface adapted to bebrought into molding relationship with the imaged surface of the matrixis raised to a sufficiently high temperature to permit ready flow intothe relieved portions to reproduce the image in otfset in the platesurface while the opposite side of the plastic sheet is at a lessertemperature suicient to permit the effect of atmospheric pressure forimage reproduction but to resist plastic flow whereby the backside ofthe plate does not constitute an exact reproduction of the image inrelief but instead remains relatively flat with only shallow valleys ordepressions, as indicated in FIGS. 4 and 5.

Under such circumstances, deformation is available in the printingsurface of the plate for complete conformance of the imaged surface ofthe matrix to reproduce the image 32a as an offset in the surfaceportion of the plate of material supplied from adjacent areas of theplastic in the sheet stock whereby the plastic in the offset portions issupplied from greater areas of the plastic sheet by comparison with thecorresponding image such that only slight valleys or depressions appearin the opposite surface of the plate, even with opposite imaged areas ofsubstantial dimension. A plate of the type described is illustrated inFIGS. 4 and 5 of the drawings. It will be apparent that the backside ofthe plastic printing plate will be relatively flat such that supportwill be available not only from the plastic but also from the backing orsupport whereby good image reproduction is available from the inkedplate without the need for filling the depressions.

Such temperature differential through the cross-section of the sheet ofplastic can be achieved by flash heating of the surface of the plasticsubsequently brought into molding relationship with the matrix, but forsuch purpose, it is preferred to make use of a sheet of plastic ofgreater cross-section ranging from 0.020 to 0.150 inch, depending uponthe type of plate that is to be produced. For a plastic plate to be usedin a newspaper printing plate where plate depth of about 0.065 inch isdesired, it is preferred to make use of a sheet of plastic having amaximum thickness of about 0.040 inch for use with an image depth ofconventional dimension of about 0.025

6 inch. For at bed presses or rotary presses used in magazine printing,sheets of plastic of greater thickness up to 0.15 inch can be used butit is preferred to make use of sheet plastic having a thickness rangingfrom 0.020 to 0.065 inch.

By way of still further modification, the slight valleys 50 or otherunevenness obtained in the backside of the plate can be substantiallycompletely avoided by the process illustrated in FIGS. 9 and 10 whereina platen 52 heated to plastic flow temperature, such as about 350 F., isbrought into engagement with the backside of the sheet of plastic 24while the opposite surface of the sheet is in molding relationship withthe imaged surface of the matrix 20. For this purpose, it is desirableto make use of a platen in the form of a flat plate having foramens 0rporosity through the cross-section thereof for exposure of theunderlying surface of the plate to the atmosphere to enable utilizationof the atmospheric effect on the upper side of the plastic sheetresponsive to suction on the underside of the plastic sheet. Further,the platen is preferably cored for the passage of heat transfer mediumtherethrough to heat the plate to a temperature for plastic deformationwhen pressed onto the backside of a sheet of plasticY material to ironout the valleys or depressions and provide a corresponding ilat surfacewhile, at the same time, pressing the sheet of plastic material intomolding relationship onto the porous matrix as an assistance in thereproduction of the image into the surface of the plastic sheet. Whenthe desired flattening operation has been achieved, coolant may becirculated through the cored platen to reduce the temperature thereoffor accelerating setting of the plastic before releasing the moldedplastic printing plate.

For such operation, it is desirable to make use of a sheet of plasticmaterial having a dimensional cross- -section such as of the typepreviously described in connection with the fabrication of a printingplate in FIGS. 4 and 5 whereby sufiicient plastic will remain beyond theoffset imaged portions for displacement 'by the platen to form theflattened surface at the backside of the plate.

Having described the manufacture of the plastic printing plate,reference will now be made briefly to one means whereby such plasticprinting plate can be mounted onto the cylinder of a printing press.Unless the sheet of plastic is originally cut to exact dimension for theplate, the edges of the formed plastic printing plate are trimmed byconventional means to the desired dimension upon completion of themolding operation.

Thereafter, the ends of the p-late are molded to extend substantiallyperpendicularly inwardly from the body portion 56 of the printing plateto provide a pair of depending flanges 58. The flanges are provided witha plurality of openings 60 spaced laterally across the plateintermediate the edges.

Referring now to FIGS. l2 and 13 as one means for mounting the plate onthe press, the plastic printing plate 56 is adapted to be mounted upon asaddle of metallic material preformed to the curvature of the platecylinder but subdivided across the center into two sections 64 and 66which are hingedly mounted at 68 onto each other for rocking movementbetween collapsed and plate position.

Pins 70 are provided in the free end walls of each of the sectionsspaced to correspond to a spaced relation between the openings 60 in theplastic printing plate and spaced inwardly from the surface of thesaddle by an amount corresponding to the distance 'between the openings60 and the body portion 56 of the plastic printing plate.

When the saddle is collapsed, as illustrated in FIG. 12, the overalldistance between the pins will be less than the length of the bodyportion of the plastic printing plate so that the pins 70 can bethreaded through the openings 60 in the flanges at the opposite ends ofthe plate. When the saddle is rocked to plate position,

illustrated in FIG. 13, the body portion of the plastic printing platewhich is dimensioned to correspond with the periphery of the saddle, ispulled taut over the surface of the saddle to bring the backside of theplate into engagement with the supporting surface of the saddle toconform the plate with the curvature of the Saddle. Means are providedon the press for clamping the saddle with the plate mounted thereon inposition of use. For removal, the saddle can be unclamped fordisplacement from the press after which the saddle can be collapsed topermit displacement of the flanges from the mounting pin for removal ofthe plastic printing plate.

With plates formed of sheet plastics having a thickness less than 0.040to 0.050 inch, the plastic printing plate will be able to assume thecurvature of the saddle without diiculty. When plates are formed ofplastic sheet stock of substantially greater thickness, it may be foundnecessary to heat the plate slightly for softening the plate or forexibilizing the plate to permit deformation to the desired curvature.Instead, the sheet of plastic material can be molded originally to thedesired curvature coincident to or separate and apart from the imagingof the plate.

It will be apparent that the described porous matrix will be well suitedto the described vacuum techniques for image reproduction into thesurface of the sheet of plastic material since such portions of thematrix as will become covered by the plastic will concentrate theexhaustion of air in portions which remain separated from the plasticsuch that the evacuated pressure forces will become maximized at theinnermost recesses and corners of the image in relief in the matrixthereby to cause entrance of the plastic into the innermost recesses forgreater detail in image reproduction. The use of a matrix of porousmaterial operates to equalize the forces throughout the cross-sectionfor greater uniformity and completeness in image transformation.

It will be understood that changes may be made in the materials employedand in the details of construction, arrangement and operation withoutdeparting from the spirit of the invention, especially as defined in thefollowing claims.

I claim:

1. A method of preparing an imaged printing plate of thermoplastic sheetmaterial comprising the steps of positioning the plastic sheet and aporous matrix in spaced parallel relation, introducing a heating meansin between the sheet and matrix for preheating the opposing surfacesthereof, withdrawing the preheating means and bringing the preheatedsurfaces together into abutting relationship, exhausting the air throughthe porous matrix from the side opposite that which is engaged by thethermoplastic sheet to generate a Vacuum between the said surfaceswhereby plastic of the sheet is der 3. The method as claimed in claim 1in which the thermoplastic sheet is dimensioned to have a thicknessWithin the range of 0.003 to 0.020 inch.

4. The method as claimed in claim 1 in which the thermoplastic sheet isdimensioned to have a thickness within the range of 0.020 to 0.040 inch.

5. The method of preparation of an imaged printing plate ofthermopiastic sheet stock comprising the steps of preheating a surfaceof a sheet of thermoplastic material, bringing the preheated surface ofthe thermoplastic sheet into abutting relationship with an imagedsurface of a porous matrix having the image in relief in the surfacethereof, exhausting air from the opposite side of the porous matrix togenerate a vacuum between the preheated surface of the thermoplasticsheet and the imaged surface of the porous matrix whereby the plastic ofthe sheet will be displaced into the recesses of the image in relief inthe porous matrix for reproduction of the image in substantiallycomplete conformance with the image in the porous matrix and as anoffset in the surface of the plastic sheet to form an imaged printingplate, pressing a heated platen having a flat face, and heated to atemperature sufficient to raise the temperature of the plastic materialto ow temperature under the pressure conditions existing, against theopposite side of the plastic stock to iron out unevenness formed in saidresponsive to displacement of plastic material into the recesses of theimage in relief in the porous matrix and separating the imaged plate ofthermoplastic material from the porous matrix after the plastic has set.

6. The method as claimed in claim 5 which includes the step of coolingthe platen prior to separating and while still in contact with theplastic sheet to set the plastic in the attened state.

7. The method as claimed in claim 5 wherein said heated platen is formedof a porous material through its cross section whereby the sheet stockin engagement with the platen will be exposed to the atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 912,092 2/ 1909Droitcour.

960,006 5/1910 Droitcour. 1,857,842 5/1932 Goldenbaum lOl-401.11,871,568 8/1932 Swan et al. 101-395 1,991,009 2/1935 Browne et al.2,078,535 4/1937 Hagedorn et al. 101-395 2,272,254 2/1942 Swan lOl-401.1X 2,345,112 3/1944 Grundel 264-89 2,400,518 5/1946 Kreber et al.lOl-401.1 X 2,512,940 6/1950 Janke lOl-415.1 2,647,284 8/1953 Richardsonet al. 101-395 X 2,678,510 5/1954 Fuerst et al. 2,970,540 2/1961 WirthlOl-415.1

DAVID KLEIN, Primary Examiner.

ROBERT A. LEIGHEY, EUGENE R. CAPOZIO,

WILLIAM B. PENN, Examiners.

1. A METHOD OF PREPARING AN IMAGED PRINTING PLATE OF THERMOPLASTIC SHEETMATERIAL COMPRISING THE STEPS OF POSITIONING THE PLASTIC SHEET AND APOROUS MATRIX IN SPACED PARALLEL RELATION, INTRODUCING A HEATING MEANSIN BETWEEN THE SHEET AND MATRIX FOR PREHEATING THE OPPOSING SURFACETHEREOF, WITHDRAWING THE PREHEATING MEANS AND BRINGING THE PREHEATEDTOGETHER INTO ABUTTING RELATIONSHIP, EXHAUSTING THE AIR THROUGH THEPOROUS MATRIX FROM THE SIDE OPPOSITE THAT WHICH IS ENGAGED BY THETHERMOPLASTIC SHEET TO GENERATE A VACUM BETWEEN THE SAID SURFACESWHEREBY PLASTIC OF THE SHEET IS DEPRESSED INTO THE RECESSES OF THE IMAGEIN RELIEF IN THE POROUS MATRIX FOR EXACT CONFORMANCE TO REPODUCE THEIMAGE IN OFFSET IN THE SURFACE OF THE PLASTIC SHEET, AND SEPARATING THEIMAGED PLASTIC SHEET FROM THE POROUS MATRIX AFTER THE PLASTIC HAS SET.